1. Field of the Invention
The invention relates to a method of determining the nuclear magnetisation distribution, where a plurality of sequences act on an examination zone in the presence of a uniform, steady magnetic field, each sequence comprising an r.f. pulse whereby, in conjunction with a magnetic gradient field, the nuclear magnetisation in the zones situated on both sides of a layer to be examined is excited and possibly dephased, and also relates to a device for performing this method.
2. Description of the Prior Art
A method and a device of this kind are known from DE-OS No. 36 04 281 corresponding to U.S. Pat. No. 4,733,184, issued Mar. 27, 1988 to the same assignee as herein, which is incorporated by reference. Therein, the nuclear magnetisation in the zones situated on both sides of a layer to be examined can be excited and dephased by means of one or two successive r.f. pulses in conjunction with a magnetic gradient field.
In the known method an amplitude-modulated r.f. pulse is generated in that in a modulator the oscillations of an oscillator are multiplied in known manner by an envelope signal which corresponds to the variation in time of the amplitude of the oscillator signal. Such an r.f. pulse has the property that the required r.f. peak power is higher as the thickness of the zone to be influenced thereby is greater. Therefore, the known method, requires comparatively high peak powers.